Resistance (Resistance Level)
The price at which a stock or market can trade, but which it cannot exceed, for a certain period of time. Often referred to as "resistance level". 
Investopedia Commentary
The stock or market stops rising because sellers start to outnumber buyers.
Related Links
Support & Resistance Basics
Support and Resistance Zones - Part 1
Support and Resistance Zones - Part 2
Introduction To Technical Analysis
See also: Breakout, Breakout Trader, Buyer's Market, Congestion, Support, Technical Analysis
Also spelled: resistance level